Blue light is required in many embodiments of LARP (Laser Activated Remote Phosphor) projection light sources. The so-called blue path usually begins at the phosphor, which is also often embodied in the form of a phosphor wheel, wherein the blue light is guided around the phosphor wheel in order to superimpose it with the light converted by the phosphor. A blue path realized in this way is disadvantageous since it requires additional space and as a result has a negative impact in terms of the production costs. Particularly for realizing light modules that are as compact as possible, for example for mobile applications, it is desirable to circumvent this blue path. One known possibility for avoiding the blue path consists in the use of polarization-rotating elements. In this case, by way of example, the excitation light is radiated via a dichroic mirror and a λ/4 plate onto a segment of the phosphor wheel that is not coated with phosphor. After passing through the λ/4 plate twice, the polarization of the blue light has rotated and can then be deflected by a dichroic beam splitter of corresponding design. The disadvantage of this solution is that polarization-rotating elements, in particular the λ/4 plates used for rotating the polarization of the excitation radiation, are expensive, however, and their use is therefore undesirable.
In another solution, a reduced etendue of the excitation source(s) emitting blue light is utilized. In order to utilize this concept with the arrangement of a light module 10 as illustrated in FIG. 1, by way of example, the dichroic mirror 12 would have to be embodied as transmissive to blue light, which then impinges on an at least partly reflective optical element 16 arranged on an optical axis 14 in an irradiation region P. After the reflection of said light, a further dichroic mirror 18 would have to be implemented to reflect this blue light. In order for this arrangement to be suitable for realizing the concept mentioned, the etendue of an excitation radiation source 22 emitting the excitation radiation 20 would accordingly have to be halved, i.e. in such a way that the excitation radiation 20 emitted by the excitation radiation source 22 impinges only on the dichroic mirror 12 but not on the dichroic mirror 18, since this portion would otherwise be lost. A reduction of the etendue is undesirable however, since excitation radiation sources with reduced etendue are associated with an undesirable reduction of permissible tolerances in the event of an increase in the excitation requirement.